In recent years, as the size of electronic equipment has reduced, increases in the level of LSI integration and the shift to ASICs has progressed rapidly, and multiple pin thin film mounting is now demanded for installing LSIs in electronic equipment, and as a result, bare chip mounting using TAB methods and flip chip methods is attracting considerable attention. In such multiple pin mounting methods, connection terminals known as bumps, which are actually projection electrodes with a height of at least 20 μm, must be arranged on the substrate with a high level of precision, and as LSIs are further miniaturized in the future, even greater levels of precision will be needed in positioning these bumps.
Furthermore, in order to aid the formation of these connection terminals, a second wiring step may be conducted for forming the wiring between the chip and the connection terminals.
Photoresists are used for forming the above connection terminals and wiring. In order to be usable within this type of application, a photoresist must be capable of forming a thick film with a thickness of at least 5 μm, for example from 5 to 20 μm, on top of the substrate. Furthermore, the photoresist must also display good adhesion to the substrate, good plating solution resistance and favorable wetting characteristics relative to the plating solution during the plating process used for forming the connection terminals and wiring, and easy removal by a stripping solution following completion of the plating process.
Furthermore, as LSIs reach even higher levels of integration, meaning the connection terminals and wiring that must be formed become even smaller, and the pitch between terminals must become even narrower, photoresists that are capable of forming space patterns with high resolution and good perpendicularity of the resist pattern side walls are becoming increasingly necessary.
As such photoresists, positive photoresist compositions comprising mainly an alkali-soluble novolak resin, and a quinonediazide group containing compound as a photosensitizer, are currently the most widely used.
However, when these types of positive photoresist compositions are used for forming a resist pattern, and a plating treatment such as gold plating is then performed to form the connection terminals and wiring pattern (the plating pattern), a problem arises in that the resist pattern develops cracks.
Because the generation of these types of cracks can cause shape abnormalities within the formed plating pattern, methods have been proposed for suppressing the generation of cracks by adding a plasticizer such as an acrylic resin to the positive photoresist composition. For example, patent reference 1 (Japanese Unexamined Patent Application, First Publication No. 2002-258479) discloses a positive photoresist composition for forming thick films, comprising an alkali-soluble novolak resin, a quinonediazide group containing compound, and an alkali-soluble acrylic resin as a plasticizer.
However, when a positive photoresist composition containing an added plasticizer is used, a variety of problems arise, including a reduction in resolution, and pattern broadening wherein the dimensions of the resist pattern following the plating process, that is, the dimensions of the plating pattern produced, are larger than the dimensions of the resist pattern immediately following developing.
An object of the present invention is to provide a positive photoresist composition capable of improving pattern broadening, and capable of forming a resist pattern with excellent resolution and good suppression of crack generation during plating, as well as a method of forming a resist pattern using such a positive photoresist composition.